Leonie, a female tiger shark has recently become very popular in various scientific circles and for a good reason. She is one of only three cases on record of asexual reproduction. Although Leonie had a few dozen pups with a male shark in the early 2000s, in 2016 she was able to give birth to three healthy pups without any assistance of a male partner.
Scientists very rarely have an opportunity to observe natural occurrences such as this one. There are only two other known cases when animals were able to do this, and that scientists have on record. One was a female eagle ray less than a year after she was separated from her male sexual partner. The other was a female boa constrictor which gave birth to parthenogenic offspring despite the fact that males were readily available for mating. In both of these cases, the time between the sexual and asexual birth was really short.
Scientists are still unclear as to how exactly this occurs. The switch happens organically and represents an amazing safety mechanism to prevent the extinction of a species. Still, this is only a temporary solution. The lack of genetic variety is like a ticking time bomb. The species is in more danger of developing debilitating mutations, and, generally, they adapt to environmental changes much slower. Another issue is that the offspring that are created by asexual reproduction are much more likely to be asexual as well.
This mechanism was probably developed out of necessity. The females passed down their genes from one female pup to the next up until males were available for reproduction.
When looking into the history of the zebra shark as a species, scientists were able to find several population bottlenecks which probably occurred during over the course of several ice ages. The theory is that the zebra sharks were able to outlive some other species simply due to the fact they were able to pump out several generations of asexual females capable of bearing offspring of their own without the participation of male sharks.
Today zebra sharks are considered an endangered species and it is highly encouraging to see that this species is capable of prolonging its existence through asexual reproduction. The only frustrating part about this is the fact that scientists are still unable to determine how exactly this switch in reproductive patterns occurs. Until they do virgin births like this one continue to stir up discussions in scientific circles.